Asthenopia is characterized by weakness or fatigue of the eyes, often accompanied by eye pain, red eyes, headache, dimming or blurring of vision and intermittent double vision. These symptoms tend to occur after tedious visual tasks such as reading or computer work. Asthenopia may be due to refractive errors, accommodation errors or abnormalities in monocular or binocular vision including myopia (nearsightedness or shortsightedness), presbyopia, farsightedness and astigmatism. Conventional treatments include the use of the eye drops containing Vitamin B1, B6 or B12, but it is not satisfied treatment.
Fatty acid derivatives are members of class of organic carboxylic acids, which are contained in tissues or organs of human or other mammals, and exhibit a wide range of physiological activity. Some fatty acid derivatives found in nature generally have a prostanoic acid skeleton as shown in the formula (A):

On the other hand, some of synthetic prostaglandin (PG) analogues have modified skeletons. The primary PGs are classified into PGAs, PGBs, PGCs, PGDs, PGEs, PGFs, PGGs, PGHs, PGIs and PGJs according to the structure of the five-membered ring moiety, and further classified into the following three types by the number and position of the unsaturated bond at the carbon chain moiety:
Subscript 1: 13,14-unsaturated-15-OH
Subscript 2: 5,6- and 13,14-diunsaturated-15-OH
Subscript 3: 5,6-, 13,14-, and 17,18-triunsaturated-15-OH.
Further, the PGFs are classified, according to the configuration of the hydroxyl group at the 9-position, into α type (the hydroxyl group is of an α-configuration) and β type (the hydroxyl group is of a β-configuration).
PGs are known to have various pharmacological and physiological activities, for example, vasodilatation, inducing of inflammation, platelet aggregation, stimulating uterine muscle, stimulating intestinal muscle, anti-ulcer effect and the like.
PGs have been known as drugs used in the ophthalmic field, for example, for lowering intraocular pressure or treating glaucoma. For example, (+)-Isopropyl (Z)-7-[(1R,2R,3R,5S)-3,5-dihydroxy-2-[(3R)-3-hydroxy-5-phenylpentyl]cyclopentyl]-5-heptenoate (general name: latanoprost), Isopropyl (5Z)-7-((1R,2R,3R,5S)-3,5-dihydroxy-2-({1E,3R)-3-hydroxy-4-[3-(trifluoromethyl) phenoxy]but-1-enyl}cyclopentyl)hept-5-enoate (general name: travoprost), (5Z)-7-{(1R,2R,3R,5S)-3,5-Dihydroxy-2-[(1E,3S)-3-hydroxy-5-phenylpent-1-en-1-yl]cyclopentyl}-N-ethylhept-5-enamide (general name: bimatoprost) and 1-Methylethyl(5Z)-7-{(1R,2R,3R,5S)-2-[(1E)-3,3-difluoro-4-phenoxy-1-butenyl]-3,5-dihydroxy cyclopentyl}-5-heptenoate (general name: tafluprost) have been marketed as ophthalmic solution for the treatment of glaucoma and/or ocular hypertension under the name of Xalatan®, Travatan®, Lumigan® and Tapros®, respectively.
Prostones, having an oxo group at position 15 of prostanoic acid skeleton (15-keto type) and having a single bond between positions 13 and 14 and an oxo group at position 15 (13,14-dihydro-15-keto type), are fatty acid derivatives known as substances naturally produced by enzymatic actions during metabolism of the primary PGs and have some therapeutic effect. Prostones have been disclosed in U.S. Pat. Nos. 5,073,569, 5,534,547, 5,225,439, 5,166,174, 5,428,062 5,380,709 5,886,034 6,265,440, 5,106,869, 5,221,763, 5,591,887, 5,770,759 and 5,739,161, the contents of these references are herein incorporated by reference.
Prostones have also been known to be useful in the ophthalmic field, for example, for lowering intraocular. pressure and treating glaucoma (U.S. Pat. Nos. 5,001,153, 5,151,444, 5,166,178, 5,194,429 and 5,236,907), for treating cataract (U.S. Pat. Nos. 5,212,324 and 5,686,487), for increasing the choroidal blood flow (U.S. Pat. No. 5,221,690), for treating optic nerve disorder (U.S. Pat. No. 5,773,471), the contents of these references are herein incorporated by reference. Ophthalmic solution comprising (+)-isopropyl (Z)-7-[(1R,2R,3R,5S)-3,5-dihydroxy-2-(3-oxodecyl)cyclopentyl]hept-5-enoate (general name: isopropyl unoprostone) has been marketed under the name of Rescula® as a pharmaceutical product for the treatment of glaucoma and ocular hypertension.
However it is not known how fatty acid derivatives act on asthenopia.